Many people’s favourite for the men’s marathon will inevitably be Kenya’s Eliud Kipchoge.
He has been the most dominant marathon runner in the world since the start of 2014 and now has five consecutive wins in top-class races to his name, all in fast times including his world-leading 2:03:05 that he ran to win in London in April.
If Kipchoge is not able to add to his 5000m bronze and silver medals respectively from the 2004 and 2008 Olympic Games, then the next best man on the 2016 world list – and the next man on many people’s list of potential gold medallists – is his compatriot Stanley Biwott.
Biwott followed Kipchoge home in April’s London Marathon in 2:03:51.
Unlike the vastly experienced Kipchoge, Biwott has never before been on a major championship team, but his consistency in big city marathons, including a hat-trick of top-four finishes in London and winning the 2012 Paris and 2015 New York marathons, suggests he should not be overawed by the occasion.
In addition to the two leading Kenyans, who will be joined by their compatriot Wesley Korir, there will be a trio of strong Ethiopian runners on the start line in Rio: Tesfaye Abera, Lemi Berhanu and Fayisa Lilesa, which means there is no room for world silver medallist Yemane Tsegay.
Abera is the fastest of the Ethiopian runners, having won the Dubai Marathon in January in 2:04:24 and is also the fastest man in the field after Kipchoge and Biwott.
He also won the Hamburg Marathon in 2:06:58 in April so can be assumed to be in good shape. However, apart from two modest outings at the World Cross Country Championships, he has never before been to a major championships.
Berhanu followed Abera home in Dubai, nine seconds in arrears, and went on to win the Boston Marathon in difficult conditions in April but also has no major championship experience other than finishing 15th in Beijing last year.
Kiprotich will defend
By contrast, one man who knows how to perform at a championship over this classic distance is Uganda's Olympic champion Stephen Kiprotich, who will defend his title in Rio.
He went on to win the 2013 world title in Moscow in fairly similar conditions to that which the runners will face at the Olympics – although Rio will be more humid than the Russia capital – proving to be the strongest as his opponents wilted in the heat.
His fourth place in Tokyo earlier in the year, his most recent marathon outing, was nothing special but enough to suggest that he will be fit enough to put up a decent defence of his title.
Kiprotich will have his compatriot Solomon Mutai, a surprise bronze medallist in Beijing, for company.
However, Olympic marathons have a habit of confounding the form book.
Who would have predicted Kiprotich would have won four years ago in London? And while 2004 and 2008 winners Stefano Baldini and Samuel Wanjiru were among the leading entrants at those Games, 1996 and 2000 winners Josia Thugwane and Gezahegn Abera were big surprises.
With the likelihood of a record field for this event as there are 155 runners on the confirmed start list, someone out of the blue – in similar fashion to the way Eritrea’s Ghirmay Ghebreslassie won in Beijing last summer – could win the men's marathon.
Ghebreslassie will also be running in Rio although history does not bode well for his chances of taking another gold as no world champion has gone on to win an Olympic title, although Abera and Kiprotich won world titles immediately after their Olympic triumphs.
The men’s marathon will be the last athletics title decided in Rio and weather conditions could play a big part in determining who will take the title. Temperatures could rise as high as 25C and humidity is likely to be about 65-70%.
Consequently, even the African runners who are used to high temperatures, although not necessarily combined with humidity, could feel the heat.
Phil Minshull for the IAAF